Imaging brain functions during neuropsychological testing

Sammanfattning: Imaging brain functions during neuropsychological testing Per Hamid Ghatan This thesis has dealt with the development of tools for assessing cognitive functions(attention and working memory) using functional imaging and the evaluation of themodulatory effects of performance, nicotine, alcohol, brain injury and auditory interference.Two cognitive tasks commonly used in the assessment of patients with brain injury,the externally-generated Perceptual Maze Test (PMT) and an internally-generated arithmeticaltask, Serial -7, were used as activation paradigms. Regional cerebral blood flowwas used as an index for neuronal activity and [ 15 O] butanol was the flow tracer.The imaging processing and statistical analysis was performed with a method developedat the Karolinska Hospital based on the computerized brain atlas and by statisticalparametric mapping (SPM). The externally-generated PMT task is a highly visuoperceptual task which elicitedcortical activations representing visuospatial decoding, attention and motor performance,with only minor involvement of the frontal cortex outside the frontal eye fields.The internally-generated Serial -7 task elicited bilateral activations in fronto-parietalregions, which reflect involvement of attention, working memory and inner speech. The PMT and the Serial -7 elicited different activation patterns representingthe recruitment of different aspects of cognition, but a similar deactivation pattern.The activations of the Serial -7 task were modulated by disturbing irrelevant speech,which may be indicative of an attention-based modulation of activity in regions attributedto task-irrelevant processing. These findings stress the importance of consideringthe activations as well as the deactivations elicited by a task when interpretingfunctional imaging data. Differences attributed to performance in the PMT were observed in regions involvedin handling different levels of perceptual complexity. Differences attributed toperformance in the Serial -7 task were found in regions that regulate aspects ofattention. These findings suggest an increased level of automaticity in high thanin low performers, the latter relied more on a higher level of perceptual processingand willed attention. Nicotine elicited a specific rCBF response in regions pertaining to attentionand vision in both non smokers and smokers. These findings are consistent with thewell-known behavioural effects of nicotine. Alcohol elicited behavioral disturbancesexpressed as CBF increases in prefrontal regions and the antenor cingulate cortexand decreases in the posterior regions. Despite these effects of nicotine and alcohol,the activation patterns elicited by the PMT and Senal -7 were unaffected. The effectof nicotine and alcohol on the anterior cingulate cortex was lateralized to the righthemisphere, which is consistent with a drug interaction with the cerebral rewardsystems. The increases with alcohol were attributed to the euphoriant effects ofthe drug, whereas the effects of nicotine may represent a more subtle effect on e.g.attention mechanisms. Patients with previous episodes of severe hypoglycaemia activated the same regionsas two control groups, when solving to the PMT task. Subtle inter-group differencesin the level of activation were however observed. The prefrontal cortex was moreactivated in patients with severe hypoglycaemia. These activations did not overlapwith those attributed to performance. When studying functional recovery after braininjury with functional imaging techniques, it is of considerable importance to usetasks and analysis that differentiate between influences from performance, compensatorystrategies as well as the restoration of function. Keywords: Keywords: Positron Emission Tomography, Cognition, Alcohol, Nicotine,Brain injury, Interference ISBN 91-628-2792-8